1. Field of the Invention
The present invention relates to a built-in-type antenna system to be mounted on a portable radio device such as a cell phone, and more particularly, to an antenna system having two elements for providing for multi-frequency-bands (hereinafter referred to as multibands).
2. Description of the Prior Art
When using a built-in-type antenna system for a compact portable radio device such as a cellphone, a mounting method thereof becomes a problem. Particularly, in the case of an antenna system having two elements for providing for multibands, its mounting method becomes a problem because the occupying portion of the system requires a large area.
Various methods are considered to mount an antenna system having two elements for providing for a multiband in the housing of a portable radio.
For example, as shown in FIGS. 6 to 8, methods for proximity-arranging two antenna elements are considered.
In FIG. 6, two coil elements 111 and 112 having element lengths different from each other are horizontally arranged. In FIG. 7, two coil elements 111 and 112 having element lengths different from each other are arranged so that they are vertically superimposed. Moreover, in FIG. 8, a coil element 111 and a linear element 132 having element lengths different from each other are horizontally arranged. Arrows in FIG. 6 to 8 show directions of antenna current.
When proximity-arranging two elements, these arrangements as shown in FIGS. 6 to 8 are advantageous for a circuit because it is possible to join one ends of these two elements and unite feeding points into one. However, in any case of FIGS. 6 to 8, because two elements are arranged in the same direction, there is a problem that communication performance is deteriorated due to the mutual interference between the elements.
To solve the above problem, a method for arranging two elements at positions as separate from each other as possible in a housing is also considered. However, this method is disadvantageous for a circuit because it is difficult to unite feeding point into one.
To solve the above problem, an antenna system is proposed in which two elements are proximity-arranged so that central axes of the elements become orthogonal to each other (refer to Patent Documents 1 and 2).
[Patent Document 1] Japanese Patent Laid-Open No. 2000-31721
[Patent Document 2] Japanese Patent Laid-Open No. 2002-319816